Electric energy is the clearest and environmentally friendly energy which is also used easily and efficiently, and is transmitted and controlled expediently.
The inductance load resistance produces reverse electromotive force for AC, so the current has a delay of 90 degrees phase angle comparing to the voltage, but the current of capacitive load leads the voltage by 90 degrees phase angle. According to this principle, the phase angle between the current and voltage in a general circuit will be reduced if a capacitor is connected in parallel to the inductance load. When cos φ=1, the current and the voltage have the same phase angle and the circuit equaling to a pure resistance. This can be achieved by paralleling a capacitor appropriately in the circuit. Such a situation is called paralleling resonance or current resonance and can achieve compensating reactive power (shown in FIG. 1, which is also called a reactive power compensation schematic diagram, and shows a parallel resonance or a current resonance circuit). When in a situation of current resonance, the current in the inductance and capacitor circuit is Q times as much as the current of power supply:Q=ωL/R ω2=1/LC                 Resonance frequency: f0=        
      1          2      ⁢                          ⁢      π        ⁢            1      LC      
Over-resonance current may damage the circuit. The current IL of inductance branch does not change too much after a capacitor is connected in parallel. Only the general circuit changes after a parallel connection between the inductance and capacitor, which raises the total power factor. The reactive current IL1 from the inductance flows into the capacitor and is stored in the capacitor, and the capacitor relieves electricity and feedback to the power supply while the inductance needs electricity. Since the flowing direction of IL1 is opposite to IC, the current I0 from the power supply will be decreased and electricity power will be saved. FIG. 2 is a phase diagram of the current and the voltage, and FIG. 3 is a power triangle diagram; φC represents a leading phase angle of capacitor and φL represents a retarding phase angle of inductance in FIG. 2.
The induction-motor, transformer and fluorescent lamp in the common agricultural equipment, such as water pump or oxygen machine, are inductance loads, and there will be an angular phase difference between the current and voltage in the circuit when the equipments being used. The larger angular phase difference becomes, the lower the power factor will be. The following can be known according to FIG. 2 and FIG. 3:                Before paralleling capacitorcos φ=P/S=P/UI0 IL=I0 IL=P/U cos φ        Reactive powerQ=S sin φ=UI0 sin φQ=UIL1         Reactive current through motor (amp.):IL1=I0×sin φ=P×sin φ/U cos φ        Current through capacitor (amp.):                    after paralleling capacitor, general circuit cos φ0≈1, sin φ0≈0, soIc≈IL1                         Capacitance (ohm):Xc=U/Ic         Capacitance (farad):C=1/ωXc         The disadvantages of low power factor are:        (1) The capacitance of power supply can not be made full use of.        (2) Power losses of the electricity transmission line, the electric generator and the transformer winding increase.        (3) Long distance transmitting electricity with low voltage causes unstable voltage. Paralleling appropriate capacitor in the inductance circuit is the most efficient and the simplest method for saving electricity.        